Process of treating incandescent-lamp filaments



Patented Aug. 17, 1926.

UNITED .STATES 1,596,246 PATENT OFFICE.

MARK N. FREDENIB'URG, F IBILOOMIEIEIJ), NEW JERSEY, .ASSIG'ITOIR. TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

PROCESS OI TREATING INCANDESCENT-LAMP FILAMENTS.

No Drawing.

My invention relates to incandescent electric lamps and, more particularly, to lamps which have filaments of refractory metal.

An object of my invention is the provision of means which tend to automatically terminate the life of an incandescent lamp when it reaches a point at which its operation becomes uneconomical.

This invention also contemplates the pro- 0 vision of means for maintaining the candle power of incandescent lamps.

. Other objects of my invention will be apparent from a reading of the following specification.

It is customary,.in the incandescent-lamp art, in speaking of the life of a lamp, to distinguish between its useful life and its burn-out life. Inasmuchas these terms are peculiar to incandescent-lam parlance and will be frequently used in this application, it is desirable to define them as hereinafterused. As 'may be inferred, the

, burn-out life refers to the number of hours of burning the lamp until failure of the filament. The usefuPlife of a lamp refers to the number of hours which it is economical to burn it. Inasmuch as. an incandescent lamp decreases in efiiciency as it burns, it is obvious that, when a lamp has fallen'in efliciency beyond a certain point, it is more economical to discard it and replace it with a new one. This economical limit of use marks the end of the useful life of the lamp.

In practical use, however,-most incandescent lamps are used throughout the burnout life, due artly to a mistaken idea of economy on the art of some users and partly to the user s lack of means for determining the economical limit in the life of the lamp.

There is a wide margin between the useful and the burn-out life of a lamp, amounting in some t es of lamps to 200% of the useful life. f

nomic waste and should, therefore, be avoided.

I have discovered means which tend to maintain the present standard for the useful life of an incandescent lamp. In other words, I have discovered means which tend to make coincident the terminations of the -burn-out life and the useful life of an incandescent lamp, while, at the same time,

his margin represents an eco-.

eliminate this wasteful margin and also to Application filed April 19, 1921. Serial No. 462,658.

providing a lamp which has a useful life equal to the present standard.

Previously known substances, called getters, used in lamps to increase their efiiciency have tended to eliminate the wasteful margin which existed in lam s not containing getters, but they have one this by improving the useful life, while my invention reduces the margin by decreasing the burnout life. Although previous getters have reduced the wasteful margin which exists in lamps not containing getters, they still leave a large margin which it is desirable to condensed on the bulb, and, being of a dark color, absorbed a considerable percentage of the light emanating from the filament. The means used in the present invention while just as effective for 1ncreasing the efficiency of the lamp as other getters used for this purpose have substantially no additional beneficial effect on the useful life but are directed to influence the burn-out life.

The present invention, by reducing the burn-out life, brings the same .closer to the useful life and thus reduces the wasteful margin. The improvement comprises the introduction of certain substances in the lamp which affect the filament in such man ner that it will tend to burn out or break when the lam has reached the end of its useful life. ore s ecifically, I have found, for example, that t e proper use of a mix ture of barium sulphate and phosphorus will accomplish the desired result, and. at the same tlme, act as a getter or beneficial agent to maintain the efliciency of the lamp. The latter action seems to be partly due to the virtue of phosphorus, which ,is well. known in the art as a valuable getter, and partly to the action of com ounds formed y the interaction of phosp orus and barium sulphate. In lieu of barium sulphate, I have successfully used other substances, such as barium phosphate. I have also successfully used certain fOlHlS'Of powdered glass alone, which may be regarded as a combination of stable oxygen-containing compounds, with the result of making the burn-out life of the lamp approach its useful life.

Still another combination which has given results similar to the previously mentioned substances has been a mixture of ferric oxide, cryolite, and phosphorus. A mixture of cryolite and phosphorus only will not ive the desired result; this fact appears to indicate the beneficial effect of ferricoxide. It appears that certain oxygen-containing compounds are necessary to r *duce the wasteful margin which exists between the terminations of the useful life and the burn-out life of the lamp.

A method of preparing a getter of the type such as is contemplated by my invention may be practiced by first mixing gms. of precipitated barium sulphate with .20 gms. of red phosphorus. To this mixture is added a solution of nitrocellulose in amylacetate, methyl alcohol, and ether, in the proportion of 1 cc. of the solution to 1 gram of the solid mixture. The solution of nitrocellulose is employed to act as a binding vehicle for the mixture of barium sulphate and phosphorus to obtain a homogeneous distribution of the mixture of phosphorus and barium sulphate in the nitrocellulose solution. The solid mixture and the solution is ball milled for 15 hours.- The filamentary material to be used in a. lamp is then passed through the nitrocellulosesolution-barium sulphate-phosphorus mixture at a predetermined rate which is dependent on the amount of the mixture desired to be applied to the filamentary material. A lamp containing afilament coated with the aforesald mixture is then exhausted of air in the usual manner without lighting the filament. After tipping off the lamp from lts exhaust tubing the coated filament is heated for the first time by applying of its rated voltage to its terminals.

It appears that the heat of the incandescent filament causes chemical changes to take place between at least some of the materials of the coating, resulting in the production of reaction products that are beneficial in maintaining the efficiency of the lamp. It would also seem that the incandescent filament is affected by the materials of the coatmg or their decomposition products in'a manner which results in a tendency of the filament to burn out when the lamp has reached the end of its useful life. While it appears that the filament is altered in some tion is not necessarily the correctone but is advanced as being a probable explanation. Tests made, on the wire, however, have shown that its tensile strength has not been impaired. as might atfirst be assumed in try ing to account for the resultant behavior of the filament in the lamp.

1 am aware that certain oxygen-containing compounds, such as metallic oxides, have been proposed for increasing the efficiency of incandescent lamps, but, so far as 1 am aware, none of the oxygen-containing compounds proposed heretofore, in fact, any other chemical substances introduced into lamps, have had the effect of making the burn-out lit'e approach the useful life.

While I have specifically named only a few substances which have the effect of making a lamp burn out when it has reached a. point when it. is uneconomical to operate it. and while I have illustrated one method of utilizing these substances, it is to be understood that other materials ma be employed and that they may be applie in various ways, but it is considered that these modifications come within the scope of my invention as outlined in the appended claims.

\Vhat is claimed is v 1. An incandescent lamp comprising a sealed envelope, a tungsten filament therein and a coating of an oxide containing material on said filament which will substantially reduce the burn-out life of the lamp and cause it to approach the useful life thereof.

2. Au incandescent lamp comprising a sealed envelope, a tungsten filament therein and a coating on said filament of a material which will increase the ratio of useful life to burn-out life of the lamp by varying both the useful life and the burn-0ut life thereof.

3. 'As an intermediate product of manufacture, an incandescent lamp filament treated with a material that acts on the burnout life of'the filament so that the normal ratio of its burn-out and useful lives is reduced substantially.

4. As an intermediate product of manufacture for incandescent electric lamps, a filament coated with a material adapted to reduce the normal ratio of the burnout life to useful life by decreasing the burnout life of the filament.

5. As an intermediate product of manufacture for incandescent lamps, a filament coated with a mixture of barium sulphate and phosphorus adapted to reduce the normal ratio of burn-out life to useful life.

6. An incandescent lamp comprising a sealed envelope, a tungsten filament therein and a substance Within said lamp capable of forming reaction products which will reduce the burn-out life of the lamp and cause it to approach the useful life thereof.

7. An incandescent lamp comprising a sealed envelope, a tungsten filament therein, and a mixture of phosphorus and barium sulphate within said lamp. 1

8. An incandescent lamp comprising a sealed envelope, a tungsten filament therein, and a mixture of phosphorus and barium sulphate applied to said filament in the form of a coating.

9. An incandescent lamp comprising. a sealed envelope, a tungsten filament therein, said filament having applied thereto a coatin of a mixture of phosphorus and bariun su phate in a nitro-cellulose solution.

10. An incandescent lamp filament having applied thereto, an oxygen-containing compound which has the pro erty of decreasing the burn-out life of the lament when'us'e in the lamp Without decreasing the useful life of the filament.

In testimony whereof, I have hereuntc subscribed my name this 18th day 01 April, 1921.

MARK N. FREDENBURG. 

